Method for containing a reticle in a pod

ABSTRACT

A method for containing a reticle in a pod is provided. The method includes opening the pod such that a pressing element retained movably on the pod by a limiting cap moves to a first position, wherein a shoulder part of the pressing element between a pressure receiving part and a pressing part of the pressing element is spaced from the limiting cap. The method further includes placing the reticle in the pod such that the reticle is pressed by the pressing element.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/798,458, which is a continuation of U.S. patent applicationSer. No. 16/232,164, filed Dec. 26^(th), 2018, which claims priority toU.S. Provisional Patent Application, No. 62/616,110, by CHIU, et al.,titled “HOLD DOWN PIN WITH FIXED TRAVEL DISTANCE,” filed Jan. 11^(th),2018, and U.S. Provisional Patent Application, No. 62/751,754, byCHUANG, et al., titled “EUV POD EIP RETICLE CONTACT POINT DESIGN,” filedOct. 29^(th), 2018, which are hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a reticle pod. More particularly, thepresent invention relates to a method for containing a reticle in anExtreme Ultraviolet (EUV) reticle pod having a reticle pressing unit.

Description of Related Art

Along with the rapid advance in semiconductor manufacturing technology,the linewidth of the semiconductor has been miniaturized, and theefficiency of the memory, the chip, the processor, or other component inthe electronic device has been drastically increased while maintainingthe size and the power consumption. A major reason of achieving theminiaturization of the linewidth is the increase in resolution of thepatterning process of the photolithography technology. In order toperform an extremely high-resolution exposure and developing process, anextreme ultraviolet light source having extremely short wavelength hasbeen used in the photolithography equipment by the industry in recentyears. Under such extreme exposure condition, the exposure environment,the semiconductor manufacturing equipment, and even the semiconductormanufacturing component all require a higher standard for cleanliness.

In order to keep the reticle clean, the reticle used in thephotolithography process is usually contained in acontamination-resistant container during manufacturing, transporting,storage, or other processing stages. The container itself is made oflow-particle-generating material and is used for isolating the reticlefrom the outside environment, preventing the reticle from beingcontacted and contaminated by outside particles or chemical gases.Generally, in advanced semiconductor fabs, the reticle container isrequired to meet the standard mechanical interface (SM IF) requirementfor cleanliness.

One known method is to utilize a dual-structure container to contain thereticle to separate the reticle from the outside environment. Asdescribed in Taiwan patent No. I501910, titled “EUV POD WITH DRAINAPPARATUS,” issued on Oct. 1st, 2015, an inner pod is used forsupporting the reticle, and an outer pod is used for fixing the innerpod. A second support element is disposed on the upper cover of theouter pod.

In the section [0024] of the disclosure and FIG. 7 of said patent, whenthe upper cover is closed, the movement of the upper cover will forcethe second support element (the element numbered 32) to press and topush down the exposed part of the fixing element (the element numbered40) in the through hole. After the fixing element 40 is pressed, it willmove further down, so the supporting pole (the element numbered 401))would also be pressed downwardly and be in contact with the four cornersof the upper surface of the reticle.

However, in said patent, the second support element 32 applies force tothe fixing element 40 in a single-point-contact manner. When the forceapplying location of the second support element 32 and the forcereceiving location of the fixing element 40 are misaligned for reasonssuch as the accumulation of assembly tolerance of the reticle pod, orany other reasons, the fixing element 40 will not be pressed evenly. Asmatter of fact, the fixing element 40 may even be tilted, and differentfixing elements 40 will have different tilted angles and will be appliedwith different forces. When the fixing elements 40 are pressed unevenly,the forces applying to the reticle from the fixing elements 40 will alsobe uneven and difficult to control. Subsequently, the reticle appliedwith uneven forces by the fixing elements 40 will crack and damageeasily and the reticle may not be held in the right position as well.Therefore, during transporting the reticle, the reticle is likelysubject to movement within the reticle pod, particles will be generated,and the reticle will be damaged easily.

Therefore, there exists a need for a reticle pod that can steadily fixthe reticle and evenly apply force to the reticle, so that theabove-mentioned problems can be solved.

SUMMARY

In view of the above-mentioned problems, the present invention is toprovide a reticle pressing unit and an EUV reticle pod using the reticlepressing unit. By using a pushing surface of an outer cover to form asurface-to-surface contact with a pressure receiving part of a pressingelement, the problems relating to a tilted pressing element and unevenforces applied to different pressing elements can be avoided. Moreover,by using the pushing surface to simultaneously press against a topsurface of a limiting cover and the pressure receiving part, the amountof the force and the travel distance of pushing can be controlled, andthe problems relating to the reticle applied with uneven forces can besolved.

According to one aspect of the invention, an EUV reticle pod isprovided. The EUV reticle pod includes an inner assembly for containingthe reticle and an outer assembly for containing the inner assembly. Theinner assembly includes a lower cover, an upper cover for engaging withthe lower cover, and a pressing unit. The lower cover includes asupporting element for supporting the reticle. The pressing unit isdisposed on the upper cover for pressing the reticle. The pressing unitincludes a pressing element and a limiting cap. The pressing element hasa pressing part and a pressure receiving part which are oppositelyarranged, and the pressing part extends through the upper cover forpressing against the reticle. The limiting cap is disposed on the uppercover and covers the pressing element, and the pressure receiving partextends through the limiting cap and is protruded outwardly from a topsurface of the limiting cap. The outer assembly includes a base and anouter cover for engaging with each other. The outer cover has a pushingsurface for forming a surface-to-surface contact with the pressurereceiving part and for simultaneously pressing against the pressurereceiving part and the top surface.

In one embodiment, the pressing element further has a shoulder partwhose two sides respectively connected to the pressure receiving partand the pressing part, and the shoulder part is confined between thelimiting cap and the upper cover. The pressing unit further includes anelastic element disposed between the upper cover, and the shoulder partis used for elastically contacting with the shoulder part. The pressingpart extends through a through hole of the upper cover, and the elasticelement has a circular structure surrounding the through hole.

In another embodiment, the pressing element further has a shoulder partwhose two sides respectively connected to the pressure receiving partand the pressing part, and the shoulder part is confined between thelimiting cap and the upper cover. The pressure receiving part extendsthrough a window of the limiting cap, and a width of the shoulder partis greater than a width of the pressure receiving part and a width ofthe window.

In yet another embodiment, the pressing element has a travel distance,and the top surface and an upper surface of the pressure receiving partare situated on the same horizontal level when the pressing elementreaches one end of the travel distance.

In a further embodiment, the reticle is touched by the pressing elementthrough one or more contact points.

In another embodiment, the reticle is touched by the supporting elementthrough one or more supporting points.

In yet another embodiment, the lower cover includes more than one of thesupporting elements disposed near the corners of the reticle, and eachcorner is supported by one of the supporting elements, and the uppercover includes more than one of the pressing units corresponding to thesupporting elements, and each corner is pressed by one of the pressingunits.

According to another aspect of the invention, a pressing unit for areticle which is configured to be used in an EUV reticle pod isprovided. The EUV reticle pod includes an outer cover, a lower cover,and an upper cover for engaging with the lower cover to contain thereticle. The pressing unit includes a pressing element and a limitingcap. The pressing element has a pressing part and a pressure receivingpart which are oppositely arranged, and the pressing part extendsthrough the upper cover for pressing against the reticle. The limitingcap is disposed on the upper cover and covers the pressing element, andthe pressure receiving part extends through the limiting cap and isprotruded outwardly from a top surface of the limiting cap. The outercover and the reticle are respectively situated on two opposite sides ofthe upper cover, and the outer cover has a pushing surface for forming asurface-to-surface contact with the pressure receiving part and forsimultaneously pressing against the pressure receiving part and the topsurface.

According to another aspect of the invention, a method for containing areticle in a pod is provided. The method includes opening the pod suchthat a pressing element retained movably on the pod by a limiting capmoves to a first position, where a shoulder part of the pressing elementbetween a pressure receiving part and a pressing part of the pressingelement is spaced from the limiting cap. The method further includesplacing the reticle in the pod such that the reticle is pressed by thepressing element.

In one embodiment, the method further includes closing the pod such thatthe pressing element moves to a second position, where the shoulder partabuts the limiting cap.

In a further embodiment, the method further includes placing the reticleon a lower cover of the pod and engaging an upper cover of the pod withthe lower cover, wherein the lower and upper covers form a firstassembly.

In a further embodiment, the method further includes placing the firstassembly on a base of the pod and engaging an outer cover of the podwith the base.

In a further embodiment, the method further includes closing the podsuch that a pushing surface of the pod presses against the pressingelement and the limiting cap.

In a further embodiment, the method further includes closing the podsuch that a plurality of contact points of the pressing element contacta top surface of the reticle.

In a further embodiment, the method further includes closing the podsuch that a plurality of supporting points of the pod contact a bottomsurface of the reticle.

According to the disclosure of the embodiments of the invention, theouter cover has the pushing surface for forming the surface-to-surfacecontact with the pressure receiving part of the pressing element, andfor simultaneously pressing against the pressure receiving part of thepressing element and the top surface of the limiting cap. Therefore, thesituation of having difficulty in controlling the amount of the forceand the travel distance of the pressing element can be prevented, anddamages on the reticle can be prevented accordingly. The problemsrelating to the reticle not being held in the right position can also besolved.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the followingdetailed description of the embodiment, with reference made to theaccompanying drawings as follows:

FIG. 1 is a perspective view of an EUV reticle pod according to oneembodiment of the invention; FIG. 2 is an exploded view of one of thepressing units of FIG. 1;

FIG. 3 is a cross-sectional view of the pressing element; FIG. 4a is aperspective view of the pushing surface contacting the pressing element;

FIG. 4b is a perspective view of the pressing element at one end of thetravel distance;

FIG. 5 is a perspective view of the pushing surface pushing at adifferent location;

FIG. 6 is a perspective view of the lower cover and the reticle of FIG.1;

FIG. 7 is a perspective view of the reticle held on the lower cover ofFIG. 6;

FIG. 8 is a perspective view of a pressing element according to anotherembodiment of the invention; and

FIG. 9 is a perspective view of a supporting element according toanother embodiment of the invention.

DETAILED DESCRIPTION

According to the embodiments of the invention, of a reticle pressingunit and an EUV reticle pod using the same, a pushing surface of anouter cover is used to form a surface-to-surface contact with a pressingelement, and the pushing surface simultaneously presses against thepressing element and a limiting cap. The pressing force and the traveldistance of the pressing element can be controlled, the excess amount ofpressure can be suppressed, and the overall pressure applying to thereticle can be limited. The problems relating to the reticle beingapplied with uneven forces can be avoided.

Please refer to FIG. 1 to FIG. 3. FIG. 1 is a perspective view of an EUVreticle pod according to one embodiment of the invention. FIG. 2 is anexploded view of one of the pressing units of FIG. 1. FIG. 3 is across-sectional view of the pressing element.

The EUV reticle pod 100 includes an inner assembly 110 and an outerassembly 150. The inner assembly 110 is used for containing a reticle Rand includes a lower cover 120 and an upper cover 130. The lower cover120 includes a supporting element 121 for supporting the reticle R. Theupper cover 130 is used for engaging with the lower cover 120 andincludes a pressing unit 140 disposed thereon for pressing the reticleR. The pressing unit 140 includes a pressing element 141 and a limitingcap 142. The pressing element 141 has a pressing part 1411 and apressure receiving part 1412 which are oppositely arranged. The pressingpart 1411 extends through the upper cover 130 to press against thereticle R. The limiting cap 142 is disposed on the upper cover 130 andcovers the pressing element 141. The limiting cap 142 has a top surface1421. The pressure receiving part 1412 extends through the limiting cap142 and is protruded upwardly from the top surface 1421. The outerassembly 150 is used for containing the inner assembly 110 and includesa base 160 and an outer cover 170 that are used for engaging with eachother. The outer cover 170 has a pushing surface 171 for forming asurface-to-surface contact with the pressure receiving part 1412, andfor simultaneously pressing against the pressure receiving part 1412 andthe top surface 1421.

In the present embodiment, the pressing element 141 further has ashoulder part 1413 whose two sides are respectively connected to thepressure receiving part 1412 and the pressing part 1411. As the pressingelement 141 covered by the limiting cap 142, the shoulder part 1413 isconfined between the limiting cap 142 and the upper cover 130, such thatthe pressing element 141 can be prevented from moving out of the two,and a travel distance of the pressing element 141 can be determined.(The way the pressing element 141 moves and its travel distance will beelaborated in the below.) In one embodiment, the pressing element 141can be exemplified by an integrally-formed structure of anerosion-resistance polymer, which not only reduces particles but alsoincreases the structural strength to properly transmit the force. Thepressing element 141 can also has the advantages including simplestructure and low manufacturing cost.

In the present embodiment, the upper cover 130 has a through hole 130 aand the limiting cap 142 has a window 142 a. The pressing part 1411extends through the through hole 130 a and the pressure receiving part1412 extends through the window 142 a. The width of the shoulder part1413 of pressing element 141 is greater than the width of the pressurereceiving part 1412 and the width of the windows 142a, so the shoulderpart 1413 can be confined between the limiting cap 142 and the uppercover 130.

The pressing unit 140 further includes an elastic element 143 disposedbetween the upper cover 130 and the shoulder part 1413 of the pressingelement 141 for elastically contacting the shoulder part 1413. Theelastic element 143 has a circular structure that surrounds the throughhole 130 a of the upper cover 130. The elastic element 143 can beexemplified by an O-ring that provides buffer while the pressing element141 is pressed and provides a certain degree of air-tightness betweenthe pressing element 141 and the upper cover 130. Therefore, thislocation will not become an airflow channel, and the overallair-tightness of the inner assembly 110 will not be affected.

In the present embodiment, the pressing unit 140 includes a firstscrewing element 144 for screwing the limiting cap 142 onto the uppercover 130. As shown in FIG. 2, the upper cover 130 has a recess 130 bcorresponding to the contour of the limiting cap 142 to receive thelimiting cap 142 and to fix the position of the limiting cap 142. Afterbeing screwed into the recess 130 b by the first screwing element 144,the limiting cap 142 can be firmly fixed and will not be shifted ormoved away from its location. In the present embodiment, the limitingcap 142 is screwed onto the upper cover 130 by way of the first screwingelement 144; however, the technology of the present invention is notlimited to the first screwing element 144; any other means for fixingthe limiting cap 142 onto the upper cover 130 are eligible to be usedherein.

Please continue referring to FIG. 1 and FIG. 2. In the EUV reticle pod100 of the present embodiment of the invention, the upper cover 130 isused for engaging with the lower cover 120 for containing the reticle R.Practically, when the reticle R is held on the lower cover 120,sometimes the reticle R is tilted due to mis-placement or mis-alignment,and one or more corners of the reticle R are not supported by one ormore supporting elements 121. The pressing unit 140 is used here topress the reticle R so that each corner of the reticle R can be properlysupported by the supporting element 121.

In one embodiment, the method of putting the reticle R into the EUVreticle pod 100 is by performed by a robotic arm and generally includesthe following steps. First, the reticle R is placed on the lower cover120, and then the upper cover 130 is brought into engagement with thelower cover 120 to form the inner assembly 110. Second, the innerassembly 110 containing reticle R therein is placed onto the base 160,and then the outer cover 170 is closed onto the base 160. While closingon the outer cover 170, the pushing surface 171 of the outer cover 170contacts and continues to push the pressing element 141, and the reticleR can be subsequently pushed into correct position by the pressingelement 141. The reticle R can be fixed by being pressed from its upperside and being supported from its lower sides by the pressing unit 140and the supporting element 121 respectively.

Please refer to FIG. 1 and FIG. 4a . FIG. 4a is a perspective view ofthe pushing surface contacting the pressing element. In the EUV reticlepod 100, the pressing element 141 pushes the reticle R to the correctposition along the travel distance of the pressing element 141. Thetravel distance of the pressing element 141 will be elaborated below.

When the outer cover 170 is brought into contact and engages with thebase 160, the pushing surface 171 of the outer cover 170 contacts thepressure receiving part 1412 of the pressing element 141. An uppersurface of the pressure receiving part 1412 is a flat surface and isused to form the surface-to-surface contact with the pushing surface171. The area of the pushing surface 171 is greater than the area of theupper surface of the pressure receiving part 1412, so the pressurereceiving part 1412 is covered entirely by the pushing surface 171 andcan be evenly pushed by the pushing surface 171. The problem of a tiltedpressing element 141 can be prevented. The pressure receiving part 1412extends through the window 142 a of the limiting cap 142 and isprotruded a distance d outwardly from the top surface 1421. At thismoment, only the pushing surface 171 contacts the pressure receivingpart 1412, and the pressing part 1411 does not contact the reticle R. Inother embodiments, the pressing part 1411 could have been in contactwith the reticle R according to the vertical location of the reticle Rbased on actual situation.

Please refer to FIG. 1 and FIG. 4b . FIG. 4b is a perspective view ofthe pressing element at one end of the travel distance. As the outercover 170 gets closer to the base 160, the pushing surface 171 continuespushing down the pressing element 141, and the pressing element 141continues pressing down the reticle R until the pressing element 141reaches one end of the travel distance. By utilizing the characteristicof vertical movement of the robotic arm, during the pressing process,the pushing surface 171 with larger area can remain thesurface-to-surface contact with the upper surface of the pressurereceiving part 1412. When the pressing element 141 reaches one end ofthe travel distance, the top surface 1421 of the limiting cap 142 andupper surface of the pressure receiving part 1412 are situated on thesame horizontal level. The pushing surface 171 simultaneously pressesagainst the pressure receiving part 1412 and the top surface 1421. Thematerial of the limiting cap 142 can be exemplified by metal, alloy, orsimilar material, which exhibits better structural strength. The topsurface 1421 of the limiting cap 142 can be regarded as the end point ofpressing the pressing element 141, i.e. one end of the travel distance,to limit the movement of the pressing element 141. To sum up, by usingthe limiting cap 142, the excess amount of pressure applied on thereticle R can be suppressed, and the pressure applied to the reticle Rcan be controlled within the design range. The upper side of the reticleR is pressed by the pressing part 1411 and the lower side of the reticleR is supported by the supporting element 121; the reticle R can befirmly fixed in this manner.

Please refer to FIG. 1, FIG. 4b , and FIG. 5. FIG. 5 is a perspectiveview of the pushing surface pushing at a different location. When theassembly tolerance of different components accumulates in the EUVreticle pod 100, the location on the top surface 1421 at which thepushing surface 171 pushes may shift. By comparison, the location atwhich the pushing surface 171′ pushes in FIG. 5 is slightly left of thelocation at which the pushing surface 171 pushes in FIG. 4b (as shown bythe dashed lines in FIG. 5). Due to the reason that the pushing surface171′ has the larger area, even when the location being pushed isshifted, the surface-to-surface contact with the upper surface of thepressure receiving part 1412 is maintained. When the pressing element141 reaches one end of the travel distance, the pushing surface 171remains surface-to-surface contact with the pressure receiving part 1412and the top surface 1421, and, equivalently, the accumulation ofassembly tolerance of components is neutralized.

As shown in FIG. 1, the outer cover 170 of the present embodiment has aprotruded stage structure, and the pushing surface 171 is the exposedsurface of the protruded stage structure. The protruded stage structureand the outer cover 170 are integrally formed in one piece. In adifferent embodiment, the outer assembly 150 includes several pushingelements disposed on the surface of the outer cover 170 facing the uppercover 130, and the pushing surface 171 is the exposed surface of thepushing elements. Practically, whether by utilizing the structure of theouter cover 170 itself or by disposing additional elements on the outercover 170, any other means for providing the pushing surface to be insurface-to-surface contact with the pressing element 141 can be used inthe present invention.

Please refer to FIG. 6 and FIG. 7 at the same time. FIG. 6 is aperspective view of the lower cover and the reticle of Fig.1. FIG. 7 isa perspective view of the reticle held on the lower cover of FIG. 6. Inthe present embodiment, the lower cover 120 includes four supportingelements 121. Each supporting element 121 is configured to be disposednear one of the four corners of the reticle R, such that each corner ofthe reticle R can be supported by one of the supporting elements 121.Each supporting element 121 has a supporting bump 1211 through which thereticle R can be supported upwardly on its lower side. The supportingelement 121 can be exemplified by an integrally formed structure oferosion resistance polymer, which not only reduces particles but alsoincreases the structural strength to properly support the reticle R onthe lower cover 120.

The lower cover 120 further includes a second screwing element 124 forscrewing the supporting elements 121 onto the lower cover 120. Although,here in the present embodiment, the supporting elements 121 are fixedonto the lower cover 120 by the second screwing element 124, thetechnology of the present invention is not limited hereto. Any othermeans for fixing the supporting elements 121 onto the lower cover 120are eligible to be used herein.

In relation to the previously-described four supporting elements 121,the upper cover 130 of the present embodiment includes four pressingunits 140 (as shown in FIG. 1) corresponding to the supporting elements121. Each corner of the reticle R is pressed by one of the pressingunits 140. The four corners of the reticle R can be supported on thelower side by the supporting elements 121 and can be pressed on theupper side by the pressing units 140. The force can be applied to thereticle R evenly, and the problems resulted from the reticle R beingapplied with uneven forces can be prevented, and the reticle R can beproperly held and fixed in the inner assembly 110.

Please continue referring to FIG. 1 and FIG. 4a . The upper cover 130 ofthe present embodiment further includes several guiding members 135. Theguiding members 135 are disposed on the upper cover 130 and configuredin a way that they extend towards the lower cover 120. The guidingmembers 135 are used for elastically contacting the peripheral of thelower cover 120. When conducting the engagement of the lower cover 120and the upper cover 130, the guiding members 135 facilitate thealignment between the two so they can be engaged with each othercorrectly. In the present embodiment, the guiding members 135 aredistributed near the four corners of the upper cover 130. However, thenumber and the disposition of the guiding members 135 are not limitedhereto. Any other means for extending toward the lower cover 120 andelastically contacting the peripheral of the lower cover 120 as theupper cover 130 engages with the lower cover 120, can be regarded as theguiding members 135 of the present invention.

In the embodiments described above with reference to FIG. 1 to FIG. 7,the reticle R is touched by the pressing element 141 through one contactpoint. To be more specific, the reticle R is touched by the tip of thepressing part 1411 of the pressing element 141 through a single-pointcontact. However, the invention is not limited by this disclosure. Thereticle R can be touched by the pressing element 141 through amulti-point contact. Please refer to FIG. 8. FIG. 8 is a perspectiveview of a pressing element according to another embodiment of theinvention. The pressing element 241 has a pressing part 2411 and apressure receiving part 2412 which are oppositely arranged, and ashoulder part 2413 whose two sides are connected to the pressing part2411 and the pressure receiving part 2412 respectively. The pressingelement 241 of FIG. 8 is different from the pressing element 141 of FIG.3 in that several contact points 2414 are disposed on the pressingelement 241. These contact points 2414 are arranged at one end of thepressing part 2411 and are substantially situated on the same horizontallevel so as to be in contact with the reticle R (reticle R is the sameas in FIG. 4b ) at the same time. By using multiple contact points 2414to touch the reticle R, the pressure applied to the reticle R per unitarea can be decreased, which further lowers the chance of damaging thereticle R and reduces particles as well.

In the embodiments described above with reference to FIG. 1 to

FIG. 7, the reticle R is touched by the supporting bump 1211 through onesupporting point. The reticle R is touched by supporting element 121through a single-point contact of the supporting bump 1211. However, theinvention is not limited by this disclosure. The reticle R can betouched by the supporting element 121 through a multi-point contact.Please refer to FIG. 9. FIG. 9 is a perspective view of a supportingelement according to another embodiment of the invention. The supportingelement 221 has a supporting bump 2211, and several supporting points2212 are disposed on and protruded from the supporting bump 2211. Thesesupporting points 2212 are substantially situated on the same horizontallevel to be in contact with the reticle R (reticle R is the same as inFIG. 4b ) at the same time. By using multiple supporting points 2212 totouch the reticle R, the pressure applied to the reticle R per unit areacan be decreased, which further lowers the chance of damaging thereticle R and reduces particles.

According to yet another embodiment of the invention, a pressing unitfor pressing a reticle is provided. The pressing unit is configured tobe used in a reticle pod. The reticle pod in the present embodiment canbe exemplified by an EUV reticle pod for containing the reticle ofextreme ultraviolet photolithography process. The reticle pod includesan outer cover, a lower cover, and an upper cover for engaging with thelower cover to contain the reticle. The pressing unit includes apressing element and a limiting cap. The pressing element has a pressingpart and a pressure receiving part which are oppositely arranged, andthe pressing part extends through the upper cover for pressing againstthe reticle. The limiting cap is disposed on the upper cover and coversthe pressing element, and the pressure receiving part extends throughthe limiting cap and is protruded outwardly from a top surface of thelimiting cap.

The outer cover and the reticle are respectively situated on twoopposite sides of the upper cover, and the outer cover has a pushingsurface for forming a surface-to-surface contact with the pressurereceiving part and for simultaneously pressing against the pressurereceiving part and the top surface. The top surface of the limiting capis regarded as one end of the travel distance of the pressing element toavoid the problems relating to excess amount of pressure. Additionally,through the surface-to-surface contact between the pushing surface andthe pressure receiving part, the pressure receiving part can be pushedevenly. The problems relating to uneven force application on thepressing element can be avoided accordingly.

According to the above-mentioned embodiments of the reticle pressingunit and EUV reticle pod using the same, the reticle pod includes theinner assembly and the outer assembly. The inner assembly includes thelower cover and the upper cover for containing the reticle. The lowercover includes the supporting element for supporting the reticle. Theupper cover is used for engaging with the lower cover and includes thepressing unit for pressing the reticle. The pressing unit includes thepressing element and the limiting cap. The pressing element has thepressing part and the pressure receiving part which are oppositelyarranged. The pressing part extends through the upper cover to pressagainst the reticle. The limiting cap is disposed on the upper cover andcovers the pressing element. The pressure receiving part extends throughthe top surface and is protruded upwardly from the top surface of thelimiting cap. The outer assembly is used for containing the innerassembly and includes the base and the outer cover which are used forengaging with each other. The outer cover has the pushing surface forforming the surface-to-surface contact with the pressure receiving part,and for pressing against the pressure receiving part and the top surfaceat the same time. Through the surface-to-surface contact between thepushing surface and the pressure receiving part of the pressing element,the problems relating to tilted pressing element and the reticle appliedwith uneven forces by different pressing elements can be avoided. Byusing the pushing surface to press against the top surface of thelimiting cap and the pressure receiving part at the same time, thetravel distance and the amount of the force can be controlled. Theexcess amount of force applying to the reticle can be suppressed, thepressure applied on the reticle can be limited, and thus the pressurecan be prevented from damaging the reticle. Moreover, since the pressingelement is covered and pressed entirely by the pushing surface, even inthe case that the pressing location is shifted, the surface-to-surfacecontact is maintained, and thus the accumulation of assembly toleranceof components can be neutralized.

The ordinal numbers used in the detailed description and claims, such as“first” and “second” do not necessarily indicate their priority ordersor up and down directions; on the contrary, they are merely intended todistinguish different elements. It will be apparent to those skilled inthe art that various modifications and variations can be made to thestructure of the present invention without departing from the scope orspirit of the invention. In view of the foregoing, it is intended thatthe present invention covers modifications and variations of thisinvention, provided they fall within the scope of the following claims.

What is claimed is:
 1. A method for containing a reticle in a pod, themethod comprising: opening the pod such that a pressing element retainedmovably on the pod by a limiting cap moves to a first position, whereina shoulder part of the pressing element between a pressure receivingpart and a pressing part of the pressing element is spaced from thelimiting cap; and placing the reticle in the pod such that the reticleis pressed by the pressing element.
 2. The method of claim 1, furthercomprising closing the pod such that the pressing element moves to asecond position, where the shoulder part abuts the limiting cap.
 3. Themethod of claim 1, further comprising: placing the reticle on a lowercover of the pod; and engaging an upper cover of the pod with the lowercover, wherein the lower and upper covers form a first assembly.
 4. Themethod of claim 3, further comprising: placing the first assembly on abase of the pod; and engaging an outer cover of the pod with the base.5. The method of claim 1, further comprising: closing the pod such thata pushing surface of the pod presses against the pressing element andthe limiting cap.
 6. The method of claim 1, further comprising: closingthe pod such that a plurality of contact points of the pressing elementcontact a top surface of the reticle.
 7. The method of claim 1, furthercomprising: closing the pod such that a plurality of supporting pointsof the pod contact a bottom surface of the reticle.